Patent GB-645069-A (GB)
Title: Telephone or similar system for establishing connections by means of group selecting
IPC: H04Q1/18
Filed: 1947-12-31
Abstract: 645,069. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. Dec. 31, 1947, No. 35116. Convention date, March 13, 1942. [Class 40 (iv)] The first outlets of the groups of outlets in a group selector and the contacts of a digit switch in the register-controller are connected to various characterising D.C. potentials, the selection being controlled by a detector as described in Specification 617,100 responding to a potential difference in the correct direction greater than a predetermined value. Provision is made for repeating the selection should a false selection. occur and for continuous hunting over the wanted group should all the outlets of this group be busy. In a 3-digit P.A.B.X., the register-controller is connected over a link-finder LS, Fig. 3, to a line-findergroup selector link, of which only the group selector GS, Fig. 4, is shown. The contacts of the banks a, b of the hundreds digit switch S and the first outlet of each group of the group selector GS are connected in parallel to tappings equally spaced, say, at a potential difference " p " on a potentiometer P. In response to the first digit, impulses from the impulsing relay AS operate the power magnet S to rotate the digit s witch. Relay LM energizes for the duration of the impulse train. When the switch moves to the first contact, earth on the wiper c completes the operating circuit for relay A which prepares the circuits for relays B, FD. Several contacts of the bank care strapped together to provide a time-lag between the setting in motion of the switch S and the group selector. If at the end of the digit the wiper c is on one of the strapped contacts, the release of LM operates relay FD to remove the earth on. the wiper c and relay B pulls up and holds in series with relay A to rotate the selector. If the digit is, e.g., 6, relay B operates when the wiper c moves off the strapped contacts to extend one end of the test wire containing the detector over the brush t of the link-finder to the wiper t of the group selector, the other end being connected over the wiper a of the switch S to the tapping 8 on the potentiometer. Operation of relay B also completes a circuit for the power magnet GS which rotates the group selector. At the end of the digit, release of relay LM removes the short-circuit on relay FD, which pulls up and sets the registercontroller for reception of the tens digit. When the selector reaches contact 51 connected to the tapping 6 on the potentiometer, the detector, which comprises a cold cathode tube, fires, since it is subjected to a potential difference of 2p, i.e., the minimum operating value, and operates relay GT to break the circuit of the magnet GS. Relay K operates and locks to disconnect the test wire from the wiper a of the switch S. Relay LC pulls up to extinguish the detector and the consequent release of relay GT removes the short-circuit from relay L which operates and holds in series with K. Relay LC releases. The test wire is now connected over wiper b of the switch S to the tapping 7, but the potential difference p between the ends of the test wire is insufficient to fire the detector. The group selector tests over brush d the outlet from contact 51, and if busy rotates until relay JT is operated over its high resistance winding by battery on the first idle outlet of the selected group to break the circuit for the magnet GS. Relay H pulls up to operate relay C and G follows, thus indicating that the group selection is completed and preparing the circuits for the final stage of selection. False selection. If after the digit 6 has been dialled the selector overshoots contact 51, owing to, e.g., dirty contacts, the detector is fired by the potential difference 3p when the selector reaches contact 61. Relays K, L operate as described above and the test wire is connected over the wiper b to the tapping 7. The detector is then fired immediately again by the potential difference 2p and relay GT pulls up to complete circuit for the operation of relay M, which breaks the operating circuits for relays JT, H and reverses the test wire connections by connecting the selector end to the tapping 9 of the potentiometer and connecting the other end to the brush t of the group selector. The detector is extinguished by the operation of relay LC and GT releases to enable relay N to pull up and hold in series with M. The circuit for relay LC is broken and the selector rotates to contact 1 where it is stopped by the operation of relay GT due to the detector being fired. Relay K falls back, LC operates to extinguish the detector and release GT, and relays L, M, N, LC release to restore the conditions existing after reception of the digit, and a fresh selection is made. All outlets of wanted group busy. The detector is fired by the potential difference 2p when the selector reaches the first outlet of the next group to reverse the test wire connections and the initial conditions are set up when the selector reaches contact 1 as is described above. The final selector stage of this system is described in Specification 645,889.